R help - Apr 2004 - Extracting numbers from somewhere within strings

Hello everybody,

I have a bunch of strings like this:
"IBM POWER4+ 1.9GHz"                  
"IBM RS64-III 500MHz"              
"IBM RS64-IV 600 MHz"                 
"IBM RS64 IV 750MHz"               
"Intel Itanium 2 Processor 6M 1.5GHz" 
"Intel Itanium2 1 Ghz"             
"Intel Itanium2 1.5GHz"               
"Intel MP 1.6GHz"                   

I want to extract the processor speed.

I am using
  grep("MHz", tpc$cpu, ignore.case=T)
  grep("GHz", tpc$cpu, ignore.case=T)
to extract the unit, because there are only these two.

But how to extract the number before it?
(I am using R 1.8.0)

In Perl one would match a regexp such as
  /([0-9.]+) ?[MG][Hh][Zz]/
and then obtain the number as $1.
But the capability of returning $1 is apparently not
implemented in grep() or any other function I could find.

How is it best done?

Thanks in advance,

  Lutz


Prof. Dr. Lutz Prechelt;  prechelt at inf.fu-berlin.de
Institut fuer Informatik; Freie Universitaet Berlin
Takustr. 9; 14195 Berlin; Germany
+49 30 838 75115; http://www.inf.fu-berlin.de/inst/ag-se/

"Lutz Prechelt" <prechelt at pcpool.mi.fu-berlin.de> writes:
> Hello everybody,
> 
> I have a bunch of strings like this:
> "IBM POWER4+ 1.9GHz"                  
> "IBM RS64-III 500MHz"              
> "IBM RS64-IV 600 MHz"                 
> "IBM RS64 IV 750MHz"               
> "Intel Itanium 2 Processor 6M 1.5GHz" 
> "Intel Itanium2 1 Ghz"             
> "Intel Itanium2 1.5GHz"               
> "Intel MP 1.6GHz"                   
> 
> I want to extract the processor speed.
> 
> I am using
>   grep("MHz", tpc$cpu, ignore.case=T)
>   grep("GHz", tpc$cpu, ignore.case=T)
> to extract the unit, because there are only these two.
> 
> But how to extract the number before it?
> (I am using R 1.8.0)
> 
> In Perl one would match a regexp such as
>   /([0-9.]+) ?[MG][Hh][Zz]/
> and then obtain the number as $1.
> But the capability of returning $1 is apparently not
> implemented in grep() or any other function I could find.
> 
> How is it best done?
> 
> Thanks in advance,
gsub() has \1 etc. For instance
> gsub("^.* ([0-9\\.]+) *[MG][Hh]z$","\\1",x)
[1] "1.9" "500" "600" "750"
"1.5" "1"   "1.5" "1.6"

(Not exactly trivial to get that right, but neither is it in Perl...)

-- 
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